<html><body>The convention is that you include parentheses if the method has <a href="http://en.wikipedia.org/wiki/Side_effect_(computer_science)">side effects</a>.

In accordance with <a href="http://en.wikipedia.org/wiki/Liskov_substitution_principle">Liskov substitution principle</a>, as overriden method is empty-paren,
the overriding method must also be declared as a method with side effects.

<small>* Refer to Programming in Scala, 5.3 Operators are methods</small>
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